Showing 261 - 270 of 2040 Items
Observation of the charmed baryon c+ and measurement of the isospin mass splittings of the c
Date: 1993-01-01
Creator: G. Crawford
C. M. Daubenmier
R. Fulton
D. Fujino
K. K., Gan
K. Honscheid
H. Kagan
R. Kass
J. Lee
R. Malchow
F. Morrow
Y. Skovpen
M. Sung
C. White
J. Whitmore
P. Wilson
F. Butler
X. Fu
G. Kalbfleisch
M. Lambrecht
W. R. Ross
P. Skubic
J. Snow
P. L. Wang
M. Wood
D. Bortoletto
D. N. Brown
J. Fast
R. L. McIlwain
T. Miao
D. H. Miller
Access: Open access
- We observe the c+ baryon decaying to Λc+π0 and measure the mass difference M(c+)-M(Λc+) to be 168.5±0.2 MeV/c2. We also measure the mass differences M(c++)-M(Λc+) and M(c0-M(Λc+) with improved precision and determine the isospin mass splittings M(c++)-M(c0) and M(c+)-M(c0) to be 1.1±0.4±0.1 MeV/c2 and 1.4±0.5±0.3 MeV/c2, respectively. Our results indicate that the light quark mass difference does not dominate the isospin mass splitting in c. © 1993 The American Physical Society.
Atmospheric potential oxygen: New observations and their implications for some atmospheric and oceanic models
Date: 2006-03-01
Creator: Mark Battle
Sara Mikaloff Fletcher
Michael L. Bender
Ralph F. Keeling
Andrew C., Manning
Nicolas Gruber
Pieter P. Tans
Melissa B. Hendricks
David T. Ho
Caroline Simonds
Robert Mika
Bill Paplawsky
Access: Open access
- Measurements of atmospheric O2/N2 ratios and CO2 concentrations can be combined into a tracer known as atmospheric potential oxygen (APO ≈ O2/N2 + CO2) that is conservative with respect to terrestrial biological activity. Consequently, APO reflects primarily ocean biogeochemistry and atmospheric circulation. Building on the work of Stephens et al. (1998), we present a set of APO observations for the years 1996-2003 with unprecedented spatial coverage. Combining data from the Princeton and Scripps air sampling programs, the data set includes new observations collected from ships in the low-latitude Pacific. The data show a smaller interhemispheric APO gradient than was observed in past studies, and different structure within the hemispheres. These differences appear to be due primarily to real changes in the APO field over time. The data also show a significant maximum in APO near the equator. Following the approach of Gruber et al. (2001), we compare these observations with predictions of APO generated from ocean O2 and CO2 flux fields and forward models of atmospheric transport. Our model predictions differ from those of earlier modeling studies, reflecting primarily the choice of atmospheric transport model (TM3 in this study). The model predictions show generally good agreement with the observations, matching the size of the interhemispheric gradient, the approximate amplitude and extent of the equatorial maximum, and the amplitude and phasing of the seasonal APO cycle at most stations. Room for improvement remains. The agreement in the interhemispheric gradient appears to be coincidental; over the last decade, the true APO gradient has evolved to a value that is consistent with our time-independent model. In addition, the equatorial maximum is somewhat more pronounced in the data than the model. This may be due to overly vigorous model transport, or insufficient spatial resolution in the air-sea fluxes used in our modeling effort. Finally, the seasonal cycles predicted by the model of atmospheric transport show evidence of an excessive seasonal rectifier in the Aleutian Islands and smaller problems elsewhere. Copyright 2006 by the American Geophysical Union.
Extinction in competitive lotka-volterra systems
Date: 1995-01-01
Creator: Mary Lou Zeeman
Access: Open access
- It is well known that for the two species autonomous competitive Lotka-Volterra model with no fixed point in the open positive quadrant, one of the species is driven to extinction, whilst the other population stabilises at its own carrying capacity. In this paper we prove a generalisation of this result to arbitrary finite dimension. That is, for the n-species autonomous competitive Lotka-Volterra model, we exhibit simple algebraic criteria on the parameters which guarantee that all but one of the species is driven to extinction, whilst the one remaining population stabilises at its own carrying capacity. © 1995 American Mathematical Society.
Atmospheric variability of methyl chloride during the last 300 years from an Antarctic ice core and firn air
Date: 2004-01-28
Creator: M. Aydin
E. S. Saltzman
W. J. De Bruyn
S. A. Montzka
J. H., Butler
M. Battle
Access: Open access
- Measurements of methyl chloride (CH3Cl) in Antarctic polar ice and firn air are used to describe the variability of atmospheric CH3Cl during the past 300 years. Firn air results from South Pole and Siple Dome suggest that the atmospheric abundance of CH3Cl increased by about 10% in the 50 years prior to 1990. Ice core measurements from Siple Dome provide evidence for a cyclic natural variability on the order of 10%, with a period of about 110 years in phase with the 20th century rise inferred from firn air. Thus, the CH3Cl increase measured in firn air may largely be a result of natural processes, which may continue to affect the atmospheric CH3Cl burden during the 21st century. Copyright 2004 by the American Geophysical Union.
Measurement of gross photosynthesis, respiration in the light, and mesophyll conductance usingh2 18o labeling
Date: 2018-05-01
Creator: Paul P.G. Gauthier
Mark O. Battle
Kevin L. Griffin
Michael L. Bender
Access: Open access
- A fundamental challenge in plant physiology is independently determining the rates of gross O2 production by photosynthesis and O2 consumption by respiration, photorespiration, and other processes. Previous studies on isolated chloroplasts or leaves have separately constrained net and gross O2 production (NOP and GOP, respectively) by labeling ambient O2 with 18O while leaf water was unlabeled. Here, we describe a method to accurately measure GOP and NOP of whole detached leaves in a cuvette as a routine gas-exchange measurement. The petiole is immersed in water enriched to a d18O of ;9,000 , and leaf water is labeled through the transpiration stream. Photosynthesis transfers 18O from H2O to O2. GOP is calculated from the increase in d18O ofO2 as air passes through the cuvette. NOP is determined from the increase in O2/N2. Both terms are measured by isotope ratio mass spectrometry. CO2 assimilation and other standard gas-exchange parameters also were measured. Reproducible measurements are made on a single leaf for more than 15 h. We used this method to measure the light response curve of NOP and GOP in French bean (Phaseolus vulgaris) at 21% and 2% O2. We then used these data to examine the O2/CO2 ratio of net photosynthesis, the light response curve of mesophyll conductance, and the apparent inhibition of respiration in the light (Kok effect) at both oxygen levels. The results are discussed in the context of evaluating the technique as a tool to study and understand leaf physiological traits.
Probing the mechanism of recognition of ssDNA by the Cdc13-DBD
Date: 2008-03-01
Creator: Aimee M. Eldridge
Deborah S. Wuttke
Access: Open access
- The Saccharomyces cerevisiae protein Cdc13 tightly and specifically binds the conserved G-rich single-stranded overhang at telomeres and plays an essential role in telomere end-protection and length regulation. The 200 residue DNA-binding domain of Cdc13 (Cdc13-DBD) binds an 11mer single-stranded representative of the yeast telomeric sequence [Tel11, d(GTGTGGGTGTG)] with a 3 pM affinity and specificity for three bases (underlined) at the 5′ end. The structure of the Cdc13-DBD bound to Tel11 revealed a large, predominantly aromatic protein interface with several unusual features. The DNA adopts an irregular, extended structure, and the binding interface includes a long (∼30 amino acids) structured loop between strands β2-β3 (L2-3) of an OB-fold. To investigate the mechanism of ssDNA binding, we studied the free and bound states of Cdc13-DBD using NMR spectroscopy. Chemical shift changes indicate that the basic topology of the domain, including L2-3, is essentially intact in the free state. Changes in slow and intermediate time scale dynamics, however, occur in L2-3, while conformational changes distant from the DNA interface suggest an induced fit mechanism for binding in the 'hot spot' for binding affinity and specificity. These data point to an overall binding mechanism well adapted to the heterogeneous nature of yeast telomeres. © 2008 The Author(s).
Precision measurement of the Ds*+-Ds+ mass difference
Date: 1994-01-01
Creator: D. N. Brown
J. Fast
R. L. McIlwain
T. Miao
D. H., Miller
M. Modesitt
D. Payne
E. I. Shibata
I. P.J. Shipsey
P. N. Wang
M. Battle
J. Ernst
Y. Kwon
S. Roberts
E. H. Thorndike
C. H. Wang
J. Dominick
M. Lambrecht
S. Sanghera
V. Shelkov
T. Skwarnicki
R. Stroynowski
I. Volobouev
G. Wei
P. Zadorozhny
M. Artuso
M. Goldberg
D. He
N. Horwitz
R. Kennett
R. Mountain
Access: Open access
- We have measured the vector-pseudoscalar mass splitting M(Ds*+)-M(Ds+)=144.220.470.37 MeV significantly more precisely than the previous world average. We minimize the systematic errors by also measuring the vector-pseudoscalar mass difference M(D*0)-M(D0) using the radiative decay D*0D0, obtaining [M(Ds*+)-M(Ds+)]-[M(D*0)-M(D0)] =2.090.470.37 MeV. This is then combined with our previous high-precision measurement of M(D*0)-M(D0), which used the decay D*0D00. We also measure the mass difference M(Ds+)-M(D+)=99.50.60.3 MeV, using the + decay modes of the Ds+ and D+ mesons. © 1994 The American Physical Society.
Observation of a new charmed strange meson
Date: 1994-01-01
Creator: Y. Kubota
M. Lattery
J. K. Nelson
S. Patton
D., Perticone
R. Poling
V. Savinov
S. Schrenk
R. Wang
M. S. Alam
I. J. Kim
B. Nemati
J. J. O'Neill
H. Severini
C. R. Sun
M. M. Zoeller
G. Crawford
C. M. Daubenmier
R. Fulton
D. Fujino
K. K. Gan
K. Honscheid
H. Kagan
R. Kass
J. Lee
R. Malchow
F. Morrow
Y. Skovpen
M. Sung
C. White
F. Butler
Access: Open access
- Using the CLEO II detector, we have obtained evidence for a new meson decaying to D0K+. Its mass is 2573.2-1.6+1.7±0.8±0.5 MeV/c2 and its width is 16-4+5±3 MeV/c2. Although we do not establish its spin and parity, the new meson is consistent with predictions for an L=1, S=1, JP=2+ charmed strange state. © 1994 The American Physical Society.
Incidence, size and spatial structure of clones in second-growth stands of coast redwood, Sequoia sempervirens (Cupressaceae)
Date: 2004-07-01
Creator: Vladimir Douhovnikoff
Adelaide M. Cheng
Richard S. Dodd
Access: Open access
- The ecology and evolutionary potential of coast redwood (Sequoia sempervirens) is significantly influenced by the important role clonal spread plays in its reproduction and site persistence. In nine second-growth stands, amplified fragment length polymorphisms (AFLPs) were used to identify redwood clonal architecture. Clones (multistem genets) dominated sites by representing an average of 70% of stems measured, ranging in size from two to 20 stems. As a result, a relatively small number of genets can monopolize a disproportionate amount of site resources, are more likely to persist over time, and have greater on-site genetic representation. Clones were not limited to fairy-ring structures, but consisted of a wide range of shapes including concentric rings, ring chains, disjunct, and linear structures. Between-ramet distances of up to 40 m were measured, indicating that clonal reproduction is not limited to basal stump resprouting. Clonal structure in second-growth stands was similar to earlier reports from old growth, emphasizing the importance of site persistence and long-term, gradual site development. Smaller ramet numbers per genet in old growth is probably due to local within-genet self thinning. Management and conservation of redwoods will benefit from a better understanding of the dynamics and structure of clonal spread in these forests.